Superconducting homopolar dynamoelectric machines

ABSTRACT

A homopolar machine having a superconducting annular field coil within which is mounted a rotor having a conductor assembly consisting of a single frustoconical conductor or a group of conductors in a frustoconical array, the outer end of the conductor assembly being located in the region of high field strength immediately within the field coil and the inner end of the conductor assembly being thus displaced axially away from the center of the coil into a region of low field strength whereby the provision of current transfer surfaces of small diameter and large axial extent with the risk of large circulating currents can be avoided.

510-10 bra FIP8502 XR Mas ues united States Patent 1151 3,639,793

Appleton et al. Feb. 1, 1972 s41 SUPERCONDUCTING HOMOPOLAR 900,77110/19os Noeggerath ..31o/17s DYNAMOELECTRIC MACHINES [72] Inventors:Anthony Derek Appleton; Michael Burke FOREIGN PATENTS OR APPLICATIONSwood; Brian Edward Mulha, a" of Foss 61,654 ll/l923 Sweden ..3l0/l78way, Newcastle upon Tyne 6, England Primary Examine'bD x sliney [22]Filed: June I, 1970 Atzorney-Kemon, Palmer & Estabrook [2!] Appl. No.:42,040 [57] ABSTRACT A homopolar machine having a superconductingannular field [30] Forms" Application Prim-y Data coil within which ismounted a rotor having a conductor as- June 2, 1969 Great Britain..27,863/69 Sembly consisting of a single fruswwnical vconductoror agroup of conductors in a frustoconical array, the outer end of 521u.s.c1 ..31o/17s,31o/10 the Conductor assembly being located in theregion of high [51] Int CL field strength immediately within the fieldcoil and the inner- 53 Field of Search ..3lO/178, 10,54 end cnductrassembly being thus disPlaced axially away from the center of the coilinto a region of low field [56] Reieremes Cited strength whereby theprovision of current transfer surfaces of small diameter and large axialextent with the risk of large cir- NIT STA PATENTS culating currents canbe avoided.

3,539,852 11/1970 Appleton et al. ..3 10/ 178 12 Claims, 3 DrawingFigures PATENTEU FEB H972 3.639.793

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PATENTEU FEB 1 I972 SHEET 2 OF 2 FIG. 2

SUPERCONDUCTING HOMOPOLAR DYNAMOELECTRIC MACHINES This invention relatesto superconducting homopolar dynamoelectric machines.

A superconducting homopolar machine with a disc-type rotor is describedin our British Pat. No. 1,133,724 in which the disc-type rotor rotatesin a magnetic field produced by a superconducting coil located in acryostat surrounding but not enclosing the rotor. In one embodiment therotor is in the form of a solid disc while in an alternative embodimentthe rotor is in the form of a number of radial conducting paths locatedon a support disc. Current transfer means are located at the peripheryof the rotor and near its axis of rotation to transfer current betweenthe rotor and an external circuit. In a typical case sliprings arelocated at the periphery of the disc and at an inner radius and brushesare arranged to contact the sliprings.

In machines of the type described where the operating currents are high,the area of contact surface between the inner slipring and brushes mustbe large and this requirement, coupled with the requirement that theinner slipring radius must be as small as possible to make maximum useof the magnetic field fiux cut by the rotor conductor or conductors,leads to theadoption of inner sliprings of substantial axial length.Losses due to circulating currents can occur at the current transfersurfaces due to the slipring surface being cut by the magnetic field,however, and it is difficult and costly to profile the long innerslipring surface to minimize these losses in the manner described incopending application Ser. No. 851,682 filed on Aug. 20, 1969.

In accordance with the present invention there is provided a homopolardynamoelectric machine having a superconducting field winding in theform of an annular field coil, a rotor mounted coaxially within thefield coil, and means for trans ferring current between a conductingpath or paths on the rotor and an external circuit, wherein the saidconducting path or paths extend between a radially outer end disposedaxially within the field coil and a radially inner end axially spacedfrom the outer end.

The outer end preferably lies on a circle centered on the rotor axis andlying in the principal plane of the field coil while the inner end,which is of smaller radius, lies in a plane normal to the rotor axis butaxially spaced from the said principal plane and preferably axiallyoutside the coil.

The conducting path on the rotor may be a continuous frustoconicalshell, analogous to the disc of a disc-type machine. Alternatively aplurality of conducting paths may be formed by segments of afrustoconical shell which are bolted or joined together, while beinginsulated from each other, to form a segmented rotor analogous to thosedescribed in our British Pat. specification No. 1,181,821. The segmentspreferably extend in the direction of the generatrix of the conicalsurface, that is to say along straight paths which, if extended, wouldall intersect the cone axis at the same point. The frustoconical shell,whether segmented or not, can be self-supporting or be mounted on anonconducting support.

In a further alternative construction the individual conducting pathscan be straight bars of rectangular or other section, tapering alongtheir length if required, instead of being segments of a frustoconicalshell. These bars can be arranged in a frustoconical array.

The support for the conducting paths can be of hollow frustoconical formwith the conducting paths on the inner surface, provision being made forconnecting the conducting paths to current transfer means on the outsideof the support.

In the drawings:

FIG. I is a partial longitudinal section of the right half of a machinein accordance with the invention;

FIG. 2 is a schematic longitudinal section ofa modification in which thetwo halves of a machine according to FIG. 1 are combined with adrum-type homopolar unit;

FIG. 3 is a diagram of connections which can be used with machinesincluding those of FIGS. 1 and 2.

Two frustoconical conductor assemblies, each of which may comprise acontinuous or segmented shell or an array of con ductor bars, can bearranged on the rotor base to base with a single field coil surroundingthe juxtaposed bases and providing the magnetic field for the twoconductor assemblies. Two such double cones, each with its own fieldcoil, can be arranged end to end to a common rotor.

In a further embodiment of the invention a frustoconical conductorassembly is placed with its base adjacent one end of a drum-shapedconductor assembly using the same field coil, thus forming a combineddrum and cone machine. A second frustoconical conductor assembly can bemounted with its base adjacent the other end of the drum assembly and asecond field coil can be arranged around the said other end to cooperatewith the first field coil in proving the field for the drum assembly.The current transfer means may be of the solid contact type, for examplecomprising brushes and sliprings, or of the liquid contact type, forexample comprising a solid contact cooperating with a mercury contact.

One form of the present invention will now be described by way ofexample with reference to the accompanying drawing, which shows avertical half section through a homopolar dynamoelectric machine inaccordance with the invention, taken on a plane including the rotoraxis.

Referring to the drawing, the machine shown in F 1G. 1, which mayoperate as a generator or a motor, comprises a superconducting statorfield coil 1 of annular shape disposed coaxial with the rotor axis XX ofthe machine and surrounding a rotor comprising two stub shafts and twofrustoconicalshaped conductor assemblies disposed base-to-base. Only theright-hand half of the machine is shown in section in the drawing, theother half being a mirror image about the plane Y-Y, and hence only onestub-shaft 2 and rotor conductor assembly 3 are visible.

The base rings of the two conductor assemblies are formed into flanges 4to allow them to be bolted base-to-base, the conductor assemblies beinginsulated from each other by insulating means, not shown. The plane ofjunction of the base rings is coplanar with the principal plane Y-Y ofthe coil 1.

Stub-shaft 2 is supported by a bearing 5 held in an end cap 6 which isin turn supported by stator structural members 7. Structural members 7also provide support for the cryostat vacuum shell 8 surrounding thecoil 1 and bear the weight of the coil 1 which is carried within aninner cryostat vessel supported by ties from the shell 8. Members 7further transmit the machine torque reaction from stationary returnconductors 9,

shaped similarly to the rotor conductor assembly and forming part of therotor circuit, to the machine foundations. Conductors 9 carry brushboxesl0 and 11 on their ends.

The frustoconical conductor assembly 3 has cantilevered sliprings l2 and13 at its radially inner and outer ends, respectively. Each slipring 12or 13 may be continuous or segmented, according to whether the rotorconductor assembly 3 comprises a single continuous path or is formed ofa number of segments providing separate rotor conducting paths. Thesliprings preferably have conical surfaces, as shown, so that the linesof flux of the stator magnetic field are generally parallel to them inorder to minimize circulating currents.

The arrangement described permits the outer slipring 13 to be positionedin an outer circumferential region of the rotor closely adjacent theprincipal plane Y-Y of the superconducting field coil, thiscircumferential region having a radius slightly smaller than the innerradius R of the field coil, and thus allows the outer end of theconductor 3 to move through that portion of the magnetic field producedby the coil 1 which has the highest llux density.

The inner slipring 12 is positioned in an inner circumferential regionof the rotor lying in a plane spaced at a distance D from the plane Y-Yand this allows the outer end of conductor 3 to extend to a region ofvery low magnetic flux density, in particular lower than would be thecase for a simple disc rotor conductor. The radius of the inner slipring12 may be considerably larger than that for a disc rotor, however, andthe area of contact surface required between slipring l2 and the brusheswhich are in contact with it may be correspondingly less, thus reducingthe transverse length of slipring surface required and minimizing anylosses due to circulating currents which can occur at the slipring tobrush interface.

The distance D would be optimized for any particular machine, dependingupon the rotor current value, stator field configuration and the desiredaxial length of the machine, but would typically lie between R and 1.5R.

in FIG. 3 is shown a developed schematic of rotor conductors In to ljextending from one end A to the other end B of a homopolar machine unit.Stationary conductors such as 7a, as indicated, connect opposite ends ofperipherally spaced rotor bars by means of brushes 50+ and 60+.

The connections leading from the rotor conductor 3 and the stationaryreturn conductor 9 to the machine terminals, and the terminalsthemselves, are not shown in the drawing, but such connections may bemade between brushboxes l and 11 or between a brushbox and returnconductor 9.

The rotor circuit of the half of the machine shown in the drawing may beconnected electrically in series with the corresponding rotor circuit ofthe half of the machine not shown.

We claim:

1. An air-cored homopolar dynamoelectric machine comprising asuperconducting field winding in the form of an annular field coil,means for maintaining said field coil at superconducting temperatures, arotor disposed coaxially within said field coil, said rotor comprisingat least one conducting path having a radially outer end located axiallywithin said field coil and closely adjacent the inner periphery of saidannular field coil and a radially inner end axially spaced from saidouter end, and means for transferring current between said conductingpath and an external circuit.

2. A homopolar machine as claimed in claim 1 wherein said rotorcomprises a plurality of conducting paths having radially outer endslocated axially within said field coil and radially inner ends locatedaxially outside said field coil, the said outer ends all lying on afirst circle centered on the rotor axis and the said inner ends alllying on a second circle centered on the rotor axis.

3. A homopolar machine as claimed in claim 2 wherein the conductingpaths conform to a frustoconical surface.

4. A homopolar machine as claimed in claim 3 in which the conductingpaths are formed by segments of a frustoconical member, said segmentsbeing secured together by electrically insulating securement means.

5. A homopolar machine as claimed in claim 1 wherein said conductingpath is of frustoconical form.

6. A homopolar machine as claimed in claim 1 wherein said currenttransfer means comprise an outer slipring on said rotor electricallyconnected to the outer end of the conducting path, an inner slipring onsaid rotor electrically connected to the inner end of the conductingpath, and fixed brushes cooperating with said outer and inner sliprings.

7. A homopolar machine as claimed in claim 6 in which the -slipringshave surfaces in contact with the brushes, said surfaces lying parallelto the magnetic field of the field coil to minimize circulating currentsin said surfaces.

8. A homopolar machine as claimed in claim 2 comprising an inner and anouter segmented slipring, each conducting path being electricallyconnected between a respective segment of the inner slipring and arespective segment of the outer slipring, a plurality of first brushescooperating with said inner slipring and a plurality of second brushescooperating with said outer slipring and a plurality of nonrotatingreturn conductors each interconnecting one of said first brushes withone of said second brushes to establish a series connection between saidconducting paths.

9. A homopolar machine as claimed in claim 1 in which said rotorcomprises at least one second conducting path having a radially outerend located adjacent said first-mentioned conducting path and a radlallylnner end disposed symmetrlcal with the radially inner end of thefirst-mentioned conducting path about the plane of the radially outerends.

10. A monopolar machine as claimed in claim 9 including means connectingthe first and second conducting paths in se- 11. A homopolar machine asclaimed in claim 2 wherein said rotor comprises a plurality of secondconducting paths having radially outer ends located adjacent theradially outer ends of the first conducting paths and radially innerends lying on a third circle centered on the rotor axis and disposed onthe side of the first circle opposite to the second circle.

12. A homopolar machine as claimed in claim 1 wherein said rotor has adrum portion having one end adjacent the radially outer end of saidconducting path and the other end remote from the radially inner end ofsaid conducting path, the drum portion carrying at least one furtherconducting path extending parallel to the axis of the rotor andcooperating with further current transfer means at the ends of the drumportion.

1. An air-cored homopolar dynamoelectric machine comprising asuperconducting field winding in the form of an annular field coil,means for maintaining said field coil at superconducting temperatures, arotor disposed coaxially within said field coil, said rotor comprisingat least one conducting path having a radially outer end located axiallywithin said field coil and closely adjacent the inner periphery of saidannular field coil and a radially inner end axially spaced from saidouter end, and means for transferring current between said conductingpath and an external circuit.
 2. A homopolar machine as claimed in claim1 wherein said rotor comprises a plurality of conducting paths havingradially outer ends located axially within said field coil and radiallyinner ends located axially outside said field coil, the said outer endsall lying on a first circle centered on the rotor axis and the saidinner ends all lying on a second circle centered on the rotor axis.
 3. Ahomopolar machine as claimed in claim 2 wherein thE conducting pathsconform to a frustoconical surface.
 4. A homopolar machine as claimed inclaim 3 in which the conducting paths are formed by segments of afrustoconical member, said segments being secured together byelectrically insulating securement means.
 5. A homopolar machine asclaimed in claim 1 wherein said conducting path is of frustoconicalform.
 6. A homopolar machine as claimed in claim 1 wherein said currenttransfer means comprise an outer slipring on said rotor electricallyconnected to the outer end of the conducting path, an inner slipring onsaid rotor electrically connected to the inner end of the conductingpath, and fixed brushes cooperating with said outer and inner sliprings.7. A homopolar machine as claimed in claim 6 in which the sliprings havesurfaces in contact with the brushes, said surfaces lying parallel tothe magnetic field of the field coil to minimize circulating currents insaid surfaces.
 8. A homopolar machine as claimed in claim 2 comprisingan inner and an outer segmented slipring, each conducting path beingelectrically connected between a respective segment of the innerslipring and a respective segment of the outer slipring, a plurality offirst brushes cooperating with said inner slipring and a plurality ofsecond brushes cooperating with said outer slipring and a plurality ofnonrotating return conductors each interconnecting one of said firstbrushes with one of said second brushes to establish a series connectionbetween said conducting paths.
 9. A homopolar machine as claimed inclaim 1 in which said rotor comprises at least one second conductingpath having a radially outer end located adjacent said first-mentionedconducting path and a radially inner end disposed symmetrical with theradially inner end of the first-mentioned conducting path about theplane of the radially outer ends.
 10. A monopolar machine as claimed inclaim 9 including means connecting the first and second conducting pathsin series.
 11. A homopolar machine as claimed in claim 2 wherein saidrotor comprises a plurality of second conducting paths having radiallyouter ends located adjacent the radially outer ends of the firstconducting paths and radially inner ends lying on a third circlecentered on the rotor axis and disposed on the side of the first circleopposite to the second circle.
 12. A homopolar machine as claimed inclaim 1 wherein said rotor has a drum portion having one end adjacentthe radially outer end of said conducting path and the other end remotefrom the radially inner end of said conducting path, the drum portioncarrying at least one further conducting path extending parallel to theaxis of the rotor and cooperating with further current transfer means atthe ends of the drum portion.